III-V materials are the materials of choice for fabricating optoelectronic emitters and detectors for a variety of applications. One reason for this is that the bandgap of the material can be chosen for the specific wavelength of interest. Fiber optic systems typically use the 1.33 μm (micrometer) and 1.50 μm wavelengths because of their transmission characteristics.
Historically, the vast majority of 1.33 μm and 1.50 μm emitters and detectors employ indium gallium arsenide (InGaAs) alloys as the emitting and detecting medium. To generate high quality InGaAs needed for an emitter or detector, it is preferred that the material be as free as possible of crystalline defects. The alloy composition and thickness of the InGaAs layers needed for functional devices necessitates growth on an indium phosphide (InP) substrate since InP has the same in-plane lattice parameter as In0.53Ga0.47As (Eg=0.75 eV at 300 K which corresponds to a wavelength of 1.65 μm).
From a cost perspective, it would be preferable to grow optoelectronic detectors and emitters on a less expensive substrate than InP, such as gallium arsenide (GaAs), germanium (Ge), or silicon (Si). However, the lattice mismatch between less expensive substrates and InGaAs alloys of desired composition results in highly defective material when grown sufficiently thick to fabricate a viable detector or emitter. Substrate cost is a significant portion of overall manufacturing cost, and therefore, finding a route to grow a material of sufficient bandgap on a less expensive substrate is of significant technical and practical interest.